Get the transparency iron-on paper you can print using a regular printer and a design from your computer. Here's a website that has it but you can probably find it locally also:
Edit: found it at Target and Jo-Anns Fabrics also!
Check out 10ShirtsFor99.com
They do FULL COLOR printing on the front, back, sides and sleeves with NO SCREEN CHARGE.
They have lots of options and upgrades. Including an option for 1 shirt. There is even an option to get the 1 shirt free.
They also do single shirt drop-shipping at